Overview: NPAC theorists seek to explain how the fundamental interactions at early times in cosmic history and at short distances gave rise to the observed properties of today's universe. For example, the universe contains more visible matter than antimatter, even more non-luminous dark matter, and a mysterious abundance of dark energy leading to cosmic acceleration. What generated these components of the cosmic energy density and how can we test our explanations? We know that new, yet unseen forces had to be present in the early universe to generate its matter and energy, but what are these forces and how might new experiments uncover them?

Similarly, we understand how the light elements such as helium were made in a process known as Big Bang nucleosynthesis, but what about heavy elements such as uranium or thorium? It is possible that they were produced in cataclysmic explosions of stars called supernovae that emitted most of their energy in neutrinos. If so, what can neutrinos tell us about these explosions occurred and the corresponding production of elements?

Finally, cosmic microwave background (CMB), large scale structure, and other cosmological observations have taught us that the state of the universe long before the time of Big Bang nucleosynthesis is consistent with a relatively elegant paradigm of cosmological initial conditions called the inflationary paradigm, but we have yet to identify which field is responsible for inflation and what the detailed dynamics of such a field is. Is it slow roll inflation? What can the possible CMB imprint of quantum gravitational fluctuations during inflation tell us about the light field degrees of freedom existing during inflation? Which models of inflation can generate large non-Guassian perturbations possibly measurable by future experiments? Are there signatures of string theory in inflationary observables? Are there equally appealing alternatives to inflation?

In short, our research can be summarized as addressing a number of unanswered questions about the universe:

• Why is there more baryon than anti-baryon in the present universe?

• What are the unseen forces present at the birth of the cosmos that disappeared from view as it evolved?

• What are the properties of neutrinos and how have they shaped the evolution of the cosmos? 

• What causes stars to explode and how were the heavy elements made? What is the nature of dark matter and dark energy? 

• Can alternative theories of gravity solve these problems and perhaps even the generic singularities existing in general relativity? 

• What is the inflaton, and what are all the physical probes of its properties? Why is the observed cosmological constant small when SM says it should be big? 

A more detailed discussion of some of our research related to these questions can be found in the following links: 

Electroweak baryogenesis and the origin of matter 

Physics beyond the Standard Model: Supersymmetry, Grand Unification, and Extra Dimensions 

Neutrino Properties and Interactions 

Neutrino Astrophysics

Electroweak Symmetry-breaking: the Higgs Boson and its Cousins

Fundamental Symmetries in Nuclei

 

Related Areas: In addition to pursuing answers to these questions, NPAC theorists also seek to explain how the properties of protons, neutrons, and atomic nuclei emerge from the strong interaction as described by Quantum Chromodynamics (QCD). Doing so is important both as a scientific quest in its own right as well as a prerequisite for interpreting the results of low-energy searches for new forces. Many of these exquisitely precise experiments involve strongly interacting systems, such as the neutron, treating them effectively as femtoscale “laboratories” for fundamental interaction studies. As with any other laboratory, it is essential to understand all the quirks of these femtoscale laboratories in order to interpret properly experimental results. More details on our research related to these areas can be found at:

Twisting the Proton in Quantum Chromodynamics: 

Effective Field Theories

 

Research Support and Synergies: External NPAC research support is provided by the Nuclear Physics and High Energy Programs of the U.S. Department of Energy Office of Science as well as the National Science Foundation. Additional external support is provided through a cooperative research agreements with Oak Ridge National Laboratory and Turkish Scientific and Technical Research Council.

The Department of Energy's Office of Science-NP  and National Science Foundation supported effort seeks to provide theoretical guidance to the “New Standard Model Initiative” (NSMI) in nuclear physics, recently identified as one of the top priorities in the 2007 Nuclear Science Advisory Committee Long Range Plan. The NSMI aims to exploit unique nuclear physics capabilities to discover key ingredients of what will be the “new” Standard Model of fundamental interactions. The experiments encompassed by the NSMI are complementary to those at the Tevatron and LHC, and will be carried out at a variety of facilities: the Spallation Neutron Source at Oak Ridge National Laboratory, Jefferson National Accelerator Facility, Brookhaven National Laboratory, Argonne National Laboratory, Los Alamos National Laboratory, and the future Deep Underground Science and Engineering Laboratory planned for the Homestake Mine. NPAC theorists are providing key theoretical leadership for the NSMI.